Controlling off-state appearance of a light emitting device

ABSTRACT

Systems for apparatuses formed of light emitting devices. Solutions for controlling the off-state appearance of lighting system designs is disclosed. Thermochromic materials are selected in accordance with a desired off-state of an LED device. The thermochromic materials are applied to a structure that is in a light path of light emitted by the LED device. In the off-state the LED device produces a desired off-state colored appearance. When the LED device is in the on-state, the thermochromic materials heat up and become more and more transparent. The light emitted from the device in its on-state does not suffer from color shifting due to the presence of the thermochromic materials. Furthermore, light emitted from the LED device in its on-state does not suffer from attenuation due to the presence of the thermochromic materials. Techniques to select and position thermochromic materials in or around LED apparatuses are presented.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/747,076, filed Jan. 23, 2018, which is a U.S. National StageEntry of International Application No. PCT/US2016/039782, filed Jun. 28,2016, which claims the benefit of priority to U.S. ProvisionalApplication No. 62/196,178, filed Jul. 23, 2015. Each of the abovepatent applications is incorporated herein by reference in its entirety.

FIELD OF INVENTION

This disclosure relates to an apparatus formed of light emitting diode(LED) devices, and more particularly to techniques for varying theoff-state color of a light emitting apparatus.

BACKGROUND

When in an off-state, light emitting devices such as light emittingdiodes (LEDs) show as the color of phosphors that have been applied onthe top of the LED chips. The phosphor might serve the purpose ofdownconverting light, however the color of the phosphor does notnecessarily match a designer's desired color, and does not necessarilymatch the color of the emitted light when the light emitting device isin an on-state. Accordingly, it is often desired to manage the off-statecolor of the LED for cosmetic reasons. An example is a translucentdiffusive layer applied over the LED of, for example, a flash unit inorder to provide a white off-state appearance. Further control of theoff-state appearance has long been desired so as to be flexible withrespect to controlling cosmetic appearances of a finished product.

Typical white LEDs consist of LED chips covered by wavelength convertingmaterials such as phosphors, dyes, or quantum dots. Because of thisstructure, phosphors are visible when the LED is powered off. Yellow- ororange-looking phosphors are often visible. Further, yellow or orangeappearances might be aesthetically in conflict with a designer'sintention. For this reason, a white diffusive layer is often applied tothe flash units. Such diffusive layers are limited to white light(translucent) to minimize the optical disadvantages such as the emissioncolor being chromatically skewed and/or the emission light intensitybeing decreased.

Improvements are needed.

SUMMARY

According to certain embodiments of the herein-disclosed techniques forcontrolling the off-state appearance of a light emitting device, amethod and apparatus are used in systems that dispose thermochromicmaterials of a selected color onto visible portions of the apparatus.

Certain embodiments are directed to technological solutions fordisposing thermochromic materials of a selected color onto theapparatus, which embodiments advance the relevant technical fields aswell as advancing peripheral technical fields. The herein-disclosedtechniques provide technical solutions that address the technicalproblems attendant to lighting system designers who want to control theoff-state appearance of designs without introducing color shifting ofthe output light and without suffering decreased light output in theon-state.

Some embodiments comprise a structure or derive from a structurecomprising a semiconductor light emitting device and thermochromicpigment that is disposed in a path of light emitted by the semiconductorlight emitting device. Some variations further comprise disposing awavelength converting material between the semiconductor light emittingdevice and the thermochromic pigment.

In some variations the thermochromic pigment is in direct contact withthe wavelength converting material.

In some variations the thermochromic pigment is spaced apart from thewavelength converting material, which variations can further comprise aheat generator in direct contact with the thermochromic pigment, andsome variations further comprise electrically-conductive wires embeddedin the thermochromic pigment and/or disposed on or embedded in aconductive glass.

Some variations further comprise a lens disposed in a path of lightemitted by the semiconductor light emitting device, wherein thethermochromic pigment is disposed on the lens. In some variations thethermochromic pigment is disposed in a transparent material.

In example variations, the thermochromic pigment undergoes a phasetransition by heating, wherein during the phase transition thethermochromic pigment changes from a colored appearance to a transparentor translucent appearance. The colored appearance is one of blue, orblack, or red.

Some embodiments are fabricated by practicing a method for forming asemiconductor light emitting device and for disposing thermochromicpigments in a path of light emitted by the semiconductor light emittingdevice. Method steps can further comprise heating the thermochromicpigment to a temperature such that the thermochromic pigment undergoes aphase transition. The heating can include positioning the thermochromicpigment such that the thermochromic pigment absorbs heat generated bythe semiconductor light emitting device or the heating can includeactivating a heat generator to heat a thermally-conductive structuralmember that is in contact with the thermochromic pigment.

Further details of aspects, objectives, and advantages of thetechnological embodiments are described herein and in the followingdescriptions, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described below are for illustration purposes only. Thedrawings are not intended to limit the scope of the present disclosure.Like reference characters shown in the figures designate the same partsin the various embodiments.

FIG. 1A presents a thermochromic material phase transition chart showingpaths for heating and cooling so as to vary the color of a lightemitting apparatus between the off-state and the on-state, according toan embodiment.

FIG. 1B is a state transition chart showing transitions between heatingand cooling so as to vary the color of a light emitting apparatusbetween the off-state and the on-state, according to some embodiments.

FIG. 1C depicts time-variant behavior of a fast-switching thermochromicmaterial in response to a varying electrical current being applied to acollocated light emitting device, according to some embodiments.

FIG. 2A depicts a semiconductor light emitting apparatus comprisingstructures that vary the color of a light emitting apparatus between theoff-state and the on-state, according to some embodiments.

FIG. 2B depicts a semiconductor light emitting apparatus havingthermochromic materials disposed on a lens so as to vary the color of alight emitting apparatus between the off-state and the on-state,according to some embodiments.

FIG. 3 is a selection chart for selecting wavelength-converting and/orthermochromic materials for varying the off-state color of a lightemitting apparatus, according to some embodiments.

FIG. 4 is a transmission spectra chart showing transmittance of athermochromic film at two temperatures, according to some embodiments.

FIG. 5A depicts time-variant performance degradation of a light emittingdevice in an air-filled environment, according to some embodiments.

FIG. 5B depicts reduced performance degradation of a light emittingdevice in an oxygen-depleted environment, according to some embodiments.

FIG. 6 depicts color-to-white transitions of an A-lamp apparatus betweenthe off-state and the on-state, according to some embodiments.

FIG. 7 depicts a color-to-transparent transition of a flash unitapparatus from the off-state to the on-state, according to someembodiments.

FIG. 8A and FIG. 8B depict methods for fabricating an apparatus inaccordance with some embodiments.

FIG. 9A, FIG. 9B and FIG. 9C depict luminaries suitable for use invarious configurations of the embodiments of the present disclosure,and/or for use in the herein-described environments.

DETAILED DESCRIPTION

Some embodiments of the present disclosure address the problem ofcontrolling the off-state appearance of lighting system designs suchthat color shifting of the output light in the on-state is eliminated orreduced and such that light output in the on-state is not undulyattenuated. Some embodiments are directed to approaches for selecting anoff-state color of thermochromic materials, and then controllingthermochromic materials through transitions from an on-state of alighting system to the off-state of the lighting system and back. Theaccompanying figures and discussions herein present example structures,devices, systems, and methods.

Overview

In embodiments of the present invention, an LED's off-state appearancemay be changed from the typical phosphor-coated appearance. In someembodiments, the off-state appearance is changed without losing any LEDfunctionality, or without losing any substantial LED functionality. Byapplying heat-sensitive pigments (called thermochromic materials) overthe LED, the off-state appearance of the LED is defined by theheat-sensitive pigments (e.g., red, green, blue, etc.) or combinationsof pigments (e.g., mixtures that combine to a black color, mixtures ofgreen and blue pigments, etc.). When the LED is powered on, heatgenerated by the LED apparatus causes a phase transition of thethermochromic materials into a transparent/translucent state such thatnormal light emission from the LED is achieved. Thermochromic pigmentscan also be spaced apart from the LED by implementing a separate heatgenerator to cause the phase transition of the thermochromic pigments,or by designing a structure where the temperature of the pigments israised to the temperature necessary for the phase transition byabsorbing light from the LED.

Various embodiments are described herein with reference to the figures.It should be noted that the figures are not necessarily drawn to scaleand that elements of similar structures or functions are sometimesrepresented by like reference characters throughout the figures. Itshould also be noted that the figures are only intended to facilitatethe description of the disclosed embodiments—they are not representativeof an exhaustive treatment of all possible embodiments, and they are notintended to impute any limitation as to the scope of the claims. Inaddition, an illustrated embodiment need not portray all aspects oradvantages of usage in any particular environment. An aspect or anadvantage described in conjunction with a particular embodiment is notnecessarily limited to that embodiment and can be practiced in any otherembodiments even if not so illustrated. References throughout thisspecification to “some embodiments” or “other embodiments” refer to aparticular feature, structure, material or characteristic described inconnection with the embodiments as being included in at least oneembodiment. Thus, the appearance of the phrases “in some embodiments” or“in other embodiments” in various places throughout this specificationare not necessarily referring to the same embodiment or embodiments.

Definitions

Some of the terms used in this description are defined below for easyreference. The presented terms and their respective definitions are notrigidly restricted to these definitions—a term may be further defined bythe term's use within this disclosure. The term “exemplary” is usedherein to mean serving as an example, instance, or illustration. Anyaspect or design described herein as “exemplary” is not necessarily tobe construed as preferred or advantageous over other aspects or designs.Rather, use of the word exemplary is intended to present concepts in aconcrete fashion. As used in this application and the appended claims,the term “or” is intended to mean an inclusive “or” rather than anexclusive “or”. That is, unless specified otherwise, or is clear fromthe context, “X employs A or B” is intended to mean any of the naturalinclusive permutations. That is, if X employs A, X employs B, or Xemploys both A and B, then “X employs A or B” is satisfied under any ofthe foregoing instances. As used herein, at least one of A or B means atleast one of A, or at least one of B, or at least one of both A and B.In other words, this phrase is disjunctive. The articles “a” and “an” asused in this application and the appended claims should generally beconstrued to mean “one or more” unless specified otherwise or is clearfrom the context to be directed to a singular form.

Reference is now made in detail to certain embodiments. The disclosedembodiments are not intended to be limiting of the claims.

Descriptions of Example Embodiments

FIG. 1A presents a thermochromic material phase transition chart 1A00showing paths for heating and cooling so as to vary the color of a lightemitting apparatus between the off-state and the on-state.

The chart shows a heating path 130 that traverses through time andtemperatures corresponding to a colored state 110, a phase transition112, and a transparent state 114. The shown temperatures and temperatureranges are merely examples of certain thermochromic materials thatchange color and transmittance as a function of temperature. Whenthermochromic materials are placed in proximity of a light emittingdiode (LED), and the proximal light emitting diode is turned on, thenthe temperature of such materials increases over time (see the abscissaof the chart). An apparatus such as an LED lamp or flash unit can beconstructed such that thermochromic materials that are placed inproximity of a heat-generating light emitting diode change phase. Onephenomenon of thermochromic materials is to change visual appearance asthe materials transition between phases.

Thermochromic materials are often based on either liquid crystals orleuco dyes. Liquid crystals are used in applications where the liquidcrystal responses are used within relatively narrow ranges oftemperatures.

Regarding liquid crystal responses, color changes result from changes ofreflectivity of certain wavelengths by the crystalline structure of thematerial. As the crystalline structure of the material changes over atemperature range (e.g., between a low-temperature crystalline phase,through an anisotropic chiral or twisted nematic phase, to ahigh-temperature isotropic liquid phase) so does the apparent color.Light passing through the crystalline structure undergoes Braggdiffraction. Wavelengths with the greatest constructive interference arereflected back, which in turn gives off a colored appearance. Changes inthe temperature of the material can result in changes of spacing betweenthe crystalline layers and therefore changes in the reflectedwavelengths. The apparent color of a thermochromic liquid crystal canrange from non-reflective (e.g., black), through the spectral colors,and into a transparent regime. The color, reflectance, and transparencycan vary depending on the temperature.

Regarding leuco dyes, such dyes are often used in applications thatdemand a wide range of colors to be used and/or when responsetemperatures need not be precise.

Considering the depiction of FIG. 1A, an LED lamp with thermochromicmaterials disposed over a bulb portion of a lamp can appear with a color(see off-state lamp 132) when at room temperature (e.g., when thethermochromic material is at or about 26° C.). After a phase transitionof the thermochromic materials that are disposed over the bulb portionof the lamp, the bulb becomes transparent when the thermochromicmaterial is at or about 120° C. (see on-state lamp 134).

When power to the LED lamp is turned off, the thermochromic materialsbegin to cool, following cooling path 140. After a phase transition ofthe thermochromic materials, the bulb begins to appear with a color.

The on-state can be maintained for any duration (e.g., while power isapplied to the LED so as to raise the temperature), and the off-statecan be maintained for any duration (e.g., while power to the LED is offso as to allow the temperature to decrease to an ambient temperature). Aseries of state transitions responsive to transitioning events is shownand described as pertains to FIG. 1B.

FIG. 1B is a state transition chart 1B00 showing transitions betweenheating and cooling so as to vary the color of a light emittingapparatus between the off-state and the on-state. The embodiment shownin FIG. 1B is merely one example involving use of athermochromic-containing colored pigment.

At state 102 (e.g., a power-off state) the solid pigment is colored. Thecolor can be controlled by selection of pigments and other materials(see FIG. 3). After a power-on event, the temperature increases. Atstate 104, the increased temperature causes a phase transition of thepigment to a liquid state. As is understood by those skilled in the art,there are many possible carriers such that the pigment remainssubstantially proximal to the LED even after transition to a liquidstate. For example, the pigment might be dispensed as a powder, and/orencapsulated in a bead or a capsule, possibly in a dye-developercombination (see FIG. 3).

When the phase transition is complete, and during the time period thatthe LED is at an elevated temperature, the liquid pigment is in a state106 that remains transparent to the light emanating from the LED. Thisstate can be maintained while the LED is at an elevated temperature(e.g., due to being powered-on). When there is a power-off event, thedecreased temperature causes a phase transition of the pigment back to asolid (see transition state 108). After a phase transition back to asolid is complete, the LED transition to the power off state, state 102,and once again the solid pigment appears as having a color.

The transition from solid to liquid and back from liquid to solid canoccur in a relatively short time period. For example, the temperature ofthe pigment can change sufficiently fast so as to cause a phase changefrom solid to liquid in a fraction of a second. The following figuredepicts a fast phase transition as a function of a time-variant currentbeing applied to a proximal light emitting device.

FIG. 1C depicts time-variant behavior of a fast-switching thermochromicmaterial 1C00 in response to a varying electrical current being appliedto a collocated light emitting device. In this embodiment threevariables change together in an in-phase relationship. Specifically, andas shown, at time T=0, a current 116 (e.g., a 2 ampere current) isapplied. The LED begins to generate light output 118 up to a maximumlight output (e.g., up to about 100% of maximum light output), and then,after the current goes to zero, the light output also goes to zero.During this time period (e.g., between T=0 ms to T=250 ms) the pigmentsthat are proximal to the light emitting device undergo theaforementioned phase transition to transparent, and then back to thecolored state. A camera flash unit can be constructed so as to behavesubstantially as depicted in FIG. 1C.

FIG. 2A depicts a semiconductor light emitting apparatus 2A00 comprisingstructures that vary the color of a light emitting apparatus between theoff-state and the on-state. As an option, one or more variations ofsemiconductor light emitting apparatus 2A00 or any aspect thereof may beimplemented in any environment and/or in any context of the embodimentsdescribed herein.

As shown a semiconductor light emitting device 222 is formed using asubmount 216, atop of which is grown n-type material 214. An activeregion 212 might be doped before disposing p-type material 210.Electrical contacts are formed on the n-type and p-type layers. When anelectrical potential of sufficient voltage is applied to the contacts(e.g., between the n-type and the p-type material), photons are emittedfrom the active region. Such photons might be substantiallymonochromatic (e.g., blue light). Some variations of semiconductor lightemitting device 222 might include a phosphor layer 208 so as to convertmonochromatic photons into photons of different energies. As such,down-converting, and in some cases up-converting photons can beengineered (e.g., by selection of wavelength-converting materials) so asto produce light that ranges across a wavelength spectrum. The phosphorlayer can be disposed proximal to the active region of the semiconductorlight emitting device, or it can be disposed remotely, such as on aninside surface of a bulb.

A thermochromic layer 202 provides structure such that an off-stateappearance may be controlled so as to be changed into a transparentappearance. Specifically, when the semiconductor light emitting deviceis powered on, heat generated by the semiconductor light emitting devicecauses a phase transition of the thermochromic materials disposed in oron the thermochromic layer such that a transparent or translucentappearance is achieved. In this and other embodiments, light emissionsare achieved without light output attenuation and without undesiredon-state chromatic shifting.

In some embodiments, thermochromic pigments can be disposed so as to bedistal from the LED by implementing a separate heat generator (e.g.,heating element 218 ₁, heating element 218 ₂) so as to cause the phasetransition of the thermochromic pigments by heating, or by designing astructure where the temperature of the pigment is raised to thetemperature necessary for the phase transition by absorbing photons fromthe LED. In some embodiments, a densified film of thermochromic pigmentsis used to enhance heat transfer from the LED to all pigment particles.Thermochromic pigments may be applied to a surface ofelectrically-conductive and/or thermally-conductive glass such as isshown in FIG. 2A as glass layer 204. An embedded conductor 220 can bedisposed on or in the glass. Strictly as one example, an indium tinoxide (ITO) glass can serve as a glass layer that is placed in the pathof light emitted by an LED. By putting electrical current through theITO glass, the glass and the applied pigments are heated by ohmic heat.Similarly, thin electrically-conductive wires can be embedded in or nearthe thermochromic pigment matrix. The thermochromic pigments can beheated by putting current through the wires. The foregoing descriptionof the glass layer is merely one example. Other structural members thatconduct heat can be used. In some embodiments, thermochromic pigmentsare in direct contact with such a structural member. The structuralmember itself can be formed of a substantially transparent material(e.g., glass) or formed of a substantially translucent material.

In some embodiments of the invention, thermochromic pigments are appliedon top of LEDs in a thermochromic pigment layer 206 on top of a phosphorlayer 208 that is disposed in an optical path of the LED active region.

Thermochromic pigments are often available in powder forms and indifferent colors. In many cases, thermochromic pigments of variouscolors are selectable based on specific phase transition temperatures.

FIG. 2B depicts a semiconductor light emitting apparatus 2B00 havingthermochromic materials disposed on a lens so as to vary the color of alight emitting apparatus between the off-state and the on-state. As anoption, one or more variations of semiconductor light emitting apparatus2B00 or any aspect thereof may be implemented in any environment and/orin any context of the embodiments described herein.

There are many possible ways of disposing the thermochromic pigments inthe optical path of the LEDs such that the thermochromic pigments areheated during operation of the LED or heating element. Thermochromicpigments 232 can be applied on a secondary optic such as, for example, alens 230. The thermochromic pigments applied to the lens absorb lightemitted by the LED when the LED is powered on. The absorption of photonsfrom the LED raises the temperature of the lens as well as thethermochromic material, which raised temperature serves to push thethermochromic material through a phase change which in turn exhibitstransparency or translucence.

In any of the foregoing embodiments, heating the thermochromic pigmentto raise the temperature can include any combinations of heating byoperation of the LED, and/or by activating a heat generator that isthermally coupled to the thermochromic pigment (e.g., by proximity, ordue to presence of the thermochromic pigment in or on athermally-conductive structural member).

A device such as is depicted in the foregoing FIG. 2A and FIG. 2B issuitable for a camera flash unit application. In such an application,the flash duration is about 200 ms. One possible design relies only onthe photons emanating from the LED to activate the phase change of thethermochromic material. Thus the switching time (e.g., the time neededfor a phase change of the thermochromic material) should be sufficientlyfast to transform the thermochromic materials to the transparent statein an early portion of the flash cycle. Such a design requirement can bemet by mixing a selected thermochromic pigment to form a carrier slurry(e.g., a silicone-based mixture) and depositing the carrier slurry on(or in proximity to) a phosphor layer of an LED. In one embodiment, ablack pigment (e.g., a black pigment with a switching temperature of 62°C.) is selected. In the same or other embodiments, other materials suchas a blue pigment (e.g., a blue pigment with a switching temperature at47° C.) can be used, and possibly mixed together with other pigments.

A given application many include a variety of design requirements thatcan influence selection of a pigment. Strictly as an example, aselection chart can be used so as to facilitate choices when mixingcolored and black pigments.

FIG. 3 is a selection chart 300 for selecting wavelength-convertingand/or thermochromic materials for varying the off-state color of alight emitting apparatus. The chart of FIG. 3 plots ranges of choicesdepicted as ovals. The ovals are arranged to approximate ranges ofswitching temperatures (e.g., lower temperatures, higher temperatures)against a spectrum of colors from red, to orange, to yellow, to green,to blue, to indigo, and through to violet. Black is also depicted.Yellow, orange and red fall into a class 302 where the body of thephosphor itself can be used to achieve a desired color appearance.Photons emanating from the LED interact with the phosphors of class 302,which interactions produce a designed-in chromatic shift.

The chart also depicts class 304 and class 306, where green and/or bluethermochromic pigments are mixed with phosphors of red, orange or yellowphosphors so as to produce a desired hue, intensity, and tint, possiblyto match to a reference color (e.g., for aesthetic purposes). Blue andblack thermochromic pigments exhibit similar switching timecharacteristics. The class 308 depicts a choice of adding blue or blackpigments to mix with other pigments and phosphors offers a wide range ofcolor choices that can be applied to an LED apparatus so as to exhibit awide range of colored off-state appearances.

The chart depicts switching temperatures from relatively lowertemperatures to relatively higher. The shown class 310 ₁ depictsrelatively lower switching temperatures while class 310 ₂ depictsrelatively higher switching temperatures.

ThermoChromic Capsules

Thermochromic pigments are often delivered as capsules that comprise adye, (e.g., a spirolactone, a spiropyran or a fluorane) that forms acolored complex with a developer (e.g., a phenolic-compound such asbisphenol-A). The dye and the developer are both present within sealedpolymeric capsules that are filled with a long chain alcohol, ester oracid. The melting point of the alcohol, ester or acid determine theswitching temperature of the dye. Upon melting, the dye-developercomplex dissociates, thus leading to discoloration of the material.Melamine or other polymers that are hard and relatively temperaturestable polymers are often used for the polymeric shell.

As earlier mentioned, it is desired that the thermochromic materialsexhibit a high degree of reflectivity (e.g., of the sought-after color)when in the solid state, and a high degree of transparency when in theliquid state. The following FIG. 4 presents scenarios where thethermochromic materials exhibit varying degrees of reflectivity over arange of visible light wavelengths.

FIG. 4 is a transmission spectra chart 400 showing transmittance of athermochromic film at two temperatures. More specifically, thetransmission spectra chart 400 depicts an example series oftransmissivity changes of a thermochromic pigment as the temperature isvaried between room temperature (e.g., 25° C.) and elevated temperatures(e.g., 150° C.). The change in appearance can be readily detected by thenaked eye or under a microscope and without using other detectionmethods.

In this example, the general shape of the curves demonstrates that thevariation in transmittance between the two temperatures is greater atrelatively lower wavelengths (e.g., in the blue-green regime). At higherwavelengths (e.g., in the orange-red regime) the thermochromic pigmentexhibits higher and higher transparency.

The shown heating transition 402 starts at a low point in the spectrumand then goes through a temperature change up to 150° C. In a coolingtransition 404 the material returns an earlier temperature and earlierstate (e.g., the dashed line). The shown transitions are merely exampletransitions.

FIG. 5A depicts time-variant performance degradation 5A00 of a lightemitting device in an air-filled environment. Thermochromic pigments areknown to degrade. The degradation can result and/or be advanced byundesirable thermal conditions and/or by undesirable photochemicalenvironments.

Photochemical Degradation

Photochemical degradation most often involves reactive oxygen speciessuch as singlet oxygen and/or radicals originating from peroxides.Remediation techniques (e.g., techniques to inhibit oxygen-relateddegradation) include introducing antioxidants and radical scavengerssuch as hindered amine light stabilizers (HALS). Another way to inhibitphotochemical degradation is to exclude oxygen from the system by theapplication of hermetic sealing layers on the layer or layers comprisingthe thermochromic capsules or on the thermochromic capsules themselves.Thin layer deposition offers a technique to protect an underlying layeror material from coming in contact with oxygen-containing gasses (e.g.,air) and/or oxygen-containing liquids (e.g., water).

Further details regarding general approaches to thin layer depositionare described in co-owned patent application publication WO2016041838.

Different applications admit of different degradation remediationtechniques. Strictly as an example application, a flash unit (e.g., fora camera) is hereunder discussed. Specific usage patterns andreliability requirements include:

-   -   A minimum of 30,000 flash cycles where the light is turned on        for about 200 ms operating under a 1 amperes drive current.    -   The temperature reaches 120° C. or more during each flash cycle.    -   Operating life is at least 168 hours of high temperature        operating life.

To achieve such stringent reliability requirements, contact between thethermochromic materials and oxygen is to be avoided

Degradation Remediation Through Exclusion of Oxygen

To demonstrate the effect of the exclusion of oxygen on degradation,switching in an air atmosphere (e.g., in a relatively oxygen-richatmosphere) is compared to switching in a nitrogen atmosphere (e.g.,relatively oxygen-poor atmosphere).

When the flash unit system is exposed to blue light in an air-filledenvironment, the transmitted intensity at high temperature decreasesover time (see decreasing trend 505). The damped shape of the curve 504indicates incomplete switching between phases and/or or browningeffects. In the specific example of FIG. 5A, the curve 504 depictsdetected blue light intensity when switching from 20° C. (at a lowintegrated intensity) to 70° C. (at a high integrated intensity) at 0.8W/cm² blue light intensity in an air-filled environment (e.g., roughly25% oxygen).

Degradation of the thermochromic material can be stopped or slowed byeliminating oxygen from the environment in which the thermochromicmaterial is disposed. One technique to eliminate oxygen is to provide anitrogen-rich atmosphere so as to purge oxygen. Evidence of reducedperformance degradation is shown and discussed as pertains to FIG. 5B.

FIG. 5B depicts reduced performance degradation 5B00 of a light emittingdevice in an oxygen-depleted environment. Specifically, the chartdepicts the same switching profile as shown and discussed as pertainingto FIG. 5A, however the conditions of FIG. 5B include a nitrogen flow.The light intensity is 0.8 W/cm2, which is the same or similar to theconditions depicted in FIG. 5A. The test conditions include a cyclebetween a period of 45 minutes in the transparent state and a period of80 minutes in the colored state. The measurements taken over thoseperiods (see curve 506) are not damped or declining. In an oxygen-poorenvironment, the device does not undergo appreciable degradation.

FIG. 6 depicts color-to-white 600 transitions of an A-lamp apparatusbetween the off-state and the on-state. As an option, one or morevariations of color-to-white 600 or any aspect thereof may beimplemented in any environment and/or in any context of the embodimentsdescribed herein.

The figure depicts two lamps that are plotted at ends of a blue-greencolor spectrum. One lamp exhibits a relatively longer wavelength color606 due to a green-appearing coating of thermochromic material beingapplied to a body formed of a translucent material 603 _(GREEN). Anotherlamp exhibits a relatively shorter wavelength color 604 due to ablue-appearing coating of thermochromic material being applied to a bodyformed of a translucent material 602 _(BLUE). When a lamp is powered on,photons from the LED strike the coating, causing a phase change of thecoating, which in turn causes a color and/or transmittance change. Asshown, the powered-on lamp has a clear or white appearing power-on state608, which may or may not be visible to the naked eye depending on theintensity of the emanated light.

Applications other than illumination lamps and camera flash units canavail of the herein-disclosed techniques. Strictly as additionalexamples, thermochromic materials can be used in filament LED lampsand/or hand-held or head-mounted flashlights and/or automotive LEDheadlamps and/or any applications where the LED module (specifically acoating on a portion of the LED module) is visible to the consumer.

FIG. 7 depicts a color-to-transparent 700 transition of a flash unitapparatus from the off-state to the on-state. As an option, one or morevariations of color-to-transparent 700 or any aspect thereof may beimplemented in any environment and/or in any context of the embodimentsdescribed herein.

As shown, a flash unit apparatus is integrated into a device 702 such asa smartphone or camera. In an off-state the flash unit apparatus has agreen appearance (see green state 704 _(GREEN)). During a power-cycle toan on-state, the thermochromic materials in or on the visible structuresof the flash unit apparatus transition to a clear state (see transparentstate 704 _(TRANSPARENT)). As such, the light emanated from the flashunit apparatus is not attenuated, and is not color shifted.

ADDITIONAL EMBODIMENTS OF THE DISCLOSURE Additional PracticalApplication Examples

FIG. 8A depicts a method 8A00 for fabricating an apparatus in accordancewith the disclosure. As shown, a semiconductor light emitting device isprovided (step 802). Wavelength-converting materials (phosphors, dyes,or quantum dots) are disposed proximal to the semiconductor lightemitting device (step 804). Based on a particular use or application forthe semiconductor light emitting device, and/or based on the intendeduse of the semiconductor light emitting device, one or morethermochromic materials are selected (step 805). The selected one ormore thermochromic materials are disposed (e.g., applied, embedded,infused, painted, adhered, loaded, etc.) with a carrier (e.g., a lens, abulb body, a glass layer, etc.) such that the thermochromic materialsare visible in an off-state of the semiconductor light emitting device(step 806). The thermochromic materials can be heated by operation ofbeing in an optical path of the photons emanated from the active region,or can be heated through a heating element. In some embodiments, a lensis placed in an optical path of photons emanating from the active region(step 808). A glass layer can be substantially flat or a glass layer canbe shaped so as to serve as a lens, or a glass layer can serve as a bulb(step 810). Such a layer (e.g., glass or other material) that is in anoptical path of photons emanating from the active region can serve as acarrier for thermochromic materials (step 812).

FIG. 8B depicts a method 8B00 for fabricating a structure in accordancewith the disclosure. As shown, a structure is assembled by providing asemiconductor light emitting device (step 820) and disposingthermochromic pigment in a path of light emitted by the semiconductorlight emitting device (step 830).

ADDITIONAL SYSTEMS EMPLOYING EMBODIMENTS OF THE DISCLOSURE AdditionalExamples

Any of the disclosed embodiments or variations thereof can be used in awide range of lighting applications and/or installation. What follows isa depiction and discussion of some example lighting applications inrepresentative installations.

FIG. 9A presents a side view of a downlight installation. As shown, thedownlight installation 902 includes a rigid or semi-rigid housing 904that supports a light emitting device array 906. The array of lightemitting devices can be organized into any arrangement, for example andas shown, into a linear array that is disposed in within the boundary ofa printed wiring board module 908. Some downlights might be composed ofmore (or fewer) instances of downlight emitters 910 in the lightemitting device array.

FIG. 9B presents a side view of a tube light emitting diode (TLED)installation. As shown, a TLED 922 includes a linear array of instancesof TLED emitters 920 that are organized so as to fit within the TLEDcavity formed by the TLED tube boundary 924. A rigid or semi-rigidhousing 926 supports a rigid or flexible substrate 928 that supports alight emitting device array 906. The rigid or flexible substrate 928 caninclude printed wiring structures (e.g., traces, thru-holes, connectors,etc.) or other electrically conductive structures disposed on one orboth sides of the rigid or flexible substrate.

FIG. 9C presents an elevation view of a troffer installation. As shown,the troffer installation 942 includes a rigid or semi-rigid shapedhousing 946 that supports an array of light emitting devices. The arrayof light emitting devices can be organized into any arrangement, forexample and as shown, into an arrangement onto a printed wiring boardmodule 908 that is disposed within the boundary of the shaped housing.Some troffers might be composed of more (or fewer) instances of lightemitting devices being populated onto the printed wiring board module.

What has been described are approaches for using thermochromic materialsof a selected color in LED-based illumination products together withtheir pertinent advantages.

Having described the invention in detail, those skilled in the art willappreciate that, given the present disclosure, modifications may be madeto the invention without departing from the spirit of the inventiveconcepts described herein. Therefore, it is not intended that the scopeof the invention be limited to the specific embodiments illustrated anddescribed.

What is being claimed is:
 1. A structure comprising: a semiconductorlight emitting device; a phosphor layer disposed on the semiconductorlight emitting device; and a thermochromic layer disposed on thephosphor layer, the thermochromic layer comprising capsules and anantioxidant, the capsules containing a leuco dye and a developer, theleuco dye and the developer forming a complex configured to dissociateupon the application of heat to the thermochromic layer, thethermochromic layer configured to be transparent or translucent when theleuco dye and the developer are dissociated and configured to have acolored appearance when the leuco dye is complexed with the developer.2. The structure of claim 1, wherein the colored appearance is a blueappearance, a black appearance, or a red appearance.
 3. The structure ofclaim 1, wherein a transition time between when the thermochromic layerhas a colored appearance and when the thermochromic layer is transparentor translucent is 250 milliseconds or less.
 4. The structure of claim 1,wherein the leuco dye is a spirolacetone, a spiropyran, or a fluorane.5. The structure of claim 1, wherein the developer is a phenoliccompound.
 6. The structure of claim 5, wherein the phenolic compound isbisphenol-A.
 7. The structure of claim 1, wherein the capsules comprisea long chain alcohol, a long chain ester, or a long chain acid.
 8. Thestructure of claim 7, wherein a melt point of the long chain alcohol,the long chain ester or the long chain acid determines the temperatureat which the leuco dye dissociates from the developer.
 9. An apparatuscomprising: a camera; and a camera flash unit comprising: asemiconductor light emitting device; a phosphor layer disposed on thesemiconductor light emitting device; and a thermochromic layer disposedon the phosphor layer, the thermochromic layer comprising capsules andan antioxidant, the capsules comprising a leuco dye and a developer, theleuco dye and the developer forming a complex configured to dissociateupon the application of heat to the thermochromic layer, thethermochromic layer having a colored appearance when the leuco dye iscomplexed with the developer and configured to be transparent ortranslucent when the leuco dye is dissociated with the developer.
 10. Astructure comprising: a semiconductor light emitting device; a phosphorlayer disposed on the semiconductor light emitting device; athermochromic layer disposed on the phosphor layer, the thermochromiclayer comprising capsules containing a leuco dye and a developer, theleuco dye and the developer forming a complex configured to dissociateupon the application of heat to the thermochromic layer, thethermochromic layer configured to be transparent or translucent when theleuco dye and the developer are dissociated and configured to have acolored appearance when the leuco dye is complexed with the developer;and hermetic sealing layers on the thermochromic layer or on thecapsules or on both.
 11. The structure of claim 10, wherein the coloredappearance is a blue appearance, a black appearance, or a redappearance.
 12. The structure of claim 10, wherein a transition timebetween when the thermochromic layer has a colored appearance and whenthe thermochromic layer is transparent or translucent is 250milliseconds or less.
 13. The structure of claim 10, wherein the leucodye is a spirolacetone, a spiropyran, or a fluorane.
 14. The structureof claim 10, wherein the developer is a phenolic compound.
 15. Thestructure of claim 10, wherein the capsules comprise a long chainalcohol, a long chain ester, or a long chain acid.
 16. The structure ofclaim 10, wherein the hermetic sealing layers is on the thermochromiclayer.
 17. The structure of claim 10, wherein the hermetic sealinglayers is on the capsules.
 18. An apparatus comprising: a camera; and acamera flash unit comprising the structure of claim
 10. 19. A lampcomprising the structure of claim
 10. 20. The structure of claim 10,wherein the thermochromic layer comprises an antioxidant.